In the past, infrared imaging and detection was mainly of interest for photon detectors used in military applications. Infrared photon detectors have excellent performance in their detection range and response time, but are very expensive and must be cooled at cryogenic temperature to insure high performance.
With today's heightened interest in security and surveillance, the civilian sector requires infrared detection and imaging; thus the market is asking for devices at lower cost. Microbolometers have become the instrument of choice for infrared imaging and detection because they are cheap and can reach quite good performances with a detection range and a response time good enough for civil applications.
The microbolometer infrared imaging industry is estimated to have a value of several hundred million dollars annually. Microbolometers are thermal sensors that operate on the principle that radiation is absorbed by a sensible material that turns temperature changes into measurable resistance changes. To have the highest sensibility, the thermal conductance between the sensible film and the substrate must be minimized. Thus, the sensible film of microbolometers is deposited on a suspended thermally insulating membrane, such as silicon nitride. To have a fast response time, the thermal capacity must be minimized.
Infrared images are maps of heat or thermal radiation. Each temperature range is assigned a visible light color to represent it, allowing the infrared measurements to be translated into an image that we can see. For example, infrared cameras detect heat radiation that can be used to “see” the heat from warm blooded animals—even at night. Deer in a forest would be invisible to an ordinary human eye or to an ordinary camera. However, an infrared camera can capture an image of such an animal that cannot be obtained from a visible light image.
FIG. 1 is an example of an infrared image. Notice the light and dark contrast of the street scene. Heated objects are light colored and cool objects are dark. Notice the contrast between the street surface which is much warmer than the vehicles moving over the surface. Notice the two vehicles on the left side of the photo about to turn right at the intersection; the contrast between the automobile and the relatively cool window glass which does not radiate much infrared light. This conveys information that the windows in both vehicles are closed. The image in FIG. 1 gives us a different view of a familiar scene, as well as information that we could not obtain from a visible light photo.
The following references reveal the state of the art in the use of semiconducting materials related to infrared imaging.
U.S. Pat. No. 6,961,168 to A. Agrawal, et al. describes durable electrooptic devices comprising ionic liquids.
U.S. Pat. No. 6,514,453 to Vigliotti et al discloses thermal sensors prepared from nanostructured powders.
U.S. Pat. No. 6,641,775 to Vigliotti et al describes reducing manufacturing and raw material costs for device manufactured with nanostructured powders.
U.S. Patent Publication 2002/0132101 to Fonash et al describes deposited thin film void-column network materials comprising a network of silicon columns in a continuous void creating a porous continuous film.
U.S. Patent Publication 2004/0005483 to Lin describes perovskite manganites for use in coatings for blocking electromagnetic interference fields (EMIs).
U.S. Patent Publication 2004/0108628 to Yadav et al describes nanostructured devices from ceramic nanomaterials.
U.S. Patent Publication 2004/0180203 to Yadav et al discloses nanomaterial compositions with distinctive shape and morphology.
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D. Zintu et al in “Dual Ion Beam Sputtering Vanadium Dioxide Microbolometers by Surface Micromachining” Infrared Physics & Technology 43 (2002) pages 254-250 describes microbolometer prototypes that are prepared using amorphous vanadium dioxide as the sensible material. The prototypes performances are close to the state of the art with detection range and response time of a few milliseconds.
The use of vanadium oxides as semiconductor materials in bolometers is discussed by Paul W. Kruse in Uncooled Thermal Energy; Arrays, Systems and Applications, Chapter 4, “Resistive Bolometers,” STIE Press, Bellingham Wash. (2002).
Improvements in semiconductor materials and other material applications require a basic improvement over normal physical limitations. It would be desirable to have more options in high performance, increased sensitivity, semiconducting materials used as temperature dependent resistors and in microbolometers for infrared imaging and detection.
The present invention provides a “drop in” replacement of semiconducting materials and a significant improvement in current semiconducting materials for resistors and microbolometer technology.